We spent Christmas & New Years 2019 - 2020 on the Gem but not that itinerary. The ship is beautifully decorated. Many other passengers wore highly festive attire -- lots of red plaid, "ugly" Christmas sweaters, totally matchy-matchy families, blinking Christmas light necklaces etc. After that cruise DH never said another word when I ask him to wear festive holiday themed socks. He was tad taken aback by some of the over the top outfits.
There was caroling in the atrium with Santa on Christmas Eve. Christmas dinner had choices of all the classics. The menus -- even in the included dinning rooms -- were stepped up for the holidays. There were plenty of two-somes like DH & I so we didn't feel lonely among the larger family groups.
New Years aboard ship is always enchanting. All holiday decorations will usually be down by January 2. It's amazing that overnight the stuff just disappears.
